1. Field of the Invention
This invention relates to a semiconductor memory device and, more particularly, a semiconductor memory that is optimistically adjusted a period of a data read time from a memory cell.
2. Description of the Related Art
In the semiconductor memory device, it is required increase a data read-out speed during the data reading operation. The data read-out operation includes some operations which selecting a memory cell of a read-out data, transferring the read-out data to internal bus and amplifying the read-out data in order to output. Accordingly, to increase a data read-out speed, a timing of starting-time of each of the operations is had to adjust.
An example of Synchronous DRAM (SDRAM) is as follows. Referring now to FIG. 1, there is shown a timing chart of operation of the SDRAM. The SDRAM latches a command at rising edge of clock signal CLOCK 101. The command is represented by combination of a row address strobe RASB 104, a column address strobe CASB 105 and write enable signal WEB 106. For example, an active command is represented as "RASB=0, CASB=1, WEB=1". In addition, the SDRAM is received a clock enable signal CKE 102 and a chip select signal CSB 103. The CKE 102 activates a command receiver which receives each of the signals 101-108. The CSB 103 selects one bank of the SDRAM from a plurality of banks which arranges on a system board. The SDRAM is received a word address signal X 109 at the same timing of the active command and received a digit address signal Y 110 at the same timing of the read or write command. In a case that a write operation, the SDRAM is received a write-data IN 111 from a data pin DQ 108. Also, a read-data OUT 112 in a read operation is outputted from the DQ 108.
Referring now to FIG. 2, there is shown a diagram of generating method of internal commands. A command receiver 201 is received the command signals, and A latch 208 latches the command signals in response to an internal clock 219 from a clock receiver 202. An internal command generator 214 generates internal commands from the RASB 104, CASB 105 and WEB 106. The X address buffer 215 latches the ADDRESS 107 in response to the active command 220, and the X address decoder 216 generates a word line selecting signal WS 222. Similarly, the Y address buffer 217 latches the ADDRESS 107 in response to the read command 221, and the Y address decoder 218 generates a digit line selecting signal DS 223. The data latch 213 is connected with an internal bus which transfers the read data from the memory cell and write data to thereof.
Referring now to FIG. 3, there is shown a circuit diagram of a memory block. The memory block includes a memory section 301, a sense amplifier register 306, Y switch circuit 310, a word line activate circuit 305, and a first data amplifier 316. Furthermore, the memory section 301 includes word lines 303-1 through 303-n, digit lines 304-1 through 304-n, and memory cells 302-11 through 302-nn which are connected an intersecting point of between each of the word lines and each of the digit lines. In reading operation, at first, the word line activate circuit 305 activates one of the word line in response to the WS 222. In the FIG. 3, the word line 303-i is activated. Accordingly, a data of the memory cells 302-1i through 302-ni are transferred to the sense amplifier resister 306. At the same time, the sense amplifier resister 306 stores the data of the memory cells 302-1i through 302-ni in response to the active command 220. Then, the Y switch circuit 310 selects one of the sense amplifier register in response to the DS 223, and the selected sense amplifier register outputs the stored data to the first data amplifier 316 through a read out line RO 315. Here, the RO 315 is used to another sense amplifier register of another memory block (refer to FIG. 4). The first data amplifier 316 outputs the stored data to a read write bus RWBUS 314 in response to a first data amplifier enable signal FAEN 317.
Referring now to FIG. 4, there is shown a circuit diagram of a prior memory device. In this FIG. 4, the memory device 401 includes four memory banks 402-405. Each of the memory banks includes a plurality of the memory blocks 421-1 through 421-n and 422-1 through 422-n. The first data amplifier 406-1 through 406-n arranges correspondly to the sense amplifier register 424-1 through 424-n and 425-1 through 425-n, respectively. Furthermore, a first data amplifier control circuit 407-1 through 407-n arranges correspondly to the first data amplifier 406-1 through 406-n, respectively. The YSW 426 is used to the memory cells 421-1 through 421-n, and the YSW 427 is used to the memory cells 422-1 through 422-n. A read control circuit 414 as a bank select circuit includes four read control circuits 415-418. Each of the read control circuits selects one bank from each of the banks.
In the case that data is read out from the memory block 421-1 of the bank 1 as follows. The read control circuit 414 is received the read command 221, and the read control circuit 415 generating a first amplifier starting signal FAS 408 in order to read the data from the bank 1. The first data amplifier control circuit 407-1 generates the FAEN 318 in response to the FAS 408. Then, the first data amplifier 406-1 outputs the stored data, or read-out data to the RWBUS 412. On the other hands, the FAS 408 is transferred to a second data amplifier control circuit 420 as a second amplifier starting signal SAS 413. The second data amplifier control circuit 420 generates a second amplifier enable signal SAEN 510 in response to the SAS 413 and outputs the SAEN 510 to a second data amplifier 419. As a results, the read-out data is read to the exterior through the data latch.
In this connection, the second data amplifier must be enabled after arriving the read-out data. Therefore, the second data amplifier control circuit 420 delayed generating the SAEN 510. Referring now to FIG. 5, there is shown a circuit diagram of the read control circuit, the first data amplifier control circuit and the second data amplifier control circuit. The read control circuit 501 is received the read command 221. The read control circuit 501 is comprised of one AND gate and six inverters, the read command 221 is delayed by the inverters of six-stages and outputted thereof as the FAS 507 or the SAS 508. Here, the signal 505 and 506 are block select signals BS which selects the memory block being indicated by the address signal. The first data amplifier control circuit 502 is comprised of two AND gates, one OR gate and three inverters. The FAS 507 is inputted to the AND gate with the BS 506. An output of AND gate is outputted as the FAEN 509 through a feed-back circuit including the OR gate, the AND gate and the inverters of three-stages and then inputted to the first data amplifier. The second data amplifier control circuit 503 is comprised of four inverters, one OR gate, one AND gate, one NAND gate and an activating timing adjusting circuit 504 composed of inverters of a plurality of stages. The SAS 508 to be inputted is inputted to the inverters of two stages, it is outputted with its delay time being adjusted at the activating timing adjusting delay circuit 504 and further inputted to the NAND gate forming the feed-back circuit. An output from the feed-back circuit is delayed in time by a predetermined amount from the SAS 508, outputted as the SAEN 510 and inputted to the second data amplifier. In addition, the number of stages of inverters in the activating timing adjusting circuit 504 is set to be adapted for a desired delay time, thereby the delay time in the activating timing adjusting circuit 504 is accurately fine adjusted and the delay time in the SAEN 510 is set to a predetermined value.
Referring now to FIG. 6, there is shown a circuit diagram of the first data amplifier. The first data amplifier 601 is received the BS 602 and FAEN 603. When the BS 602 becomes the high level and the FAEN 603 becomes low-level, the first data amplifier 601 amplifies the stored data by the sense amplifier register through the RO lines which is ROT 604 and RON 605. Then, the amplified data is outputted to the RWBUS which is RWBUSTj 606 and RWBUSNj 607.
Referring now to FIG. 7, there is shown a circuit diagram of the second data amplifier. The second data amplifier 701 is received the PBTB 702 and SAEN 703. The PBTB 702 indicates a timing of precharging the RWBUS, the RWBUS is prechaged when the PBTB 702 becomes high-level. When the PBTB 702 and SAEN 703 becomes low-level, the second data amplifier 701 amplifies the amplified data by the first data amplifier register through the RWBUSTj 704 and RWBUSNj 705. Then, the amplified data is outputted as the read-out data DATi 706.
Referring now to FIG. 8, there is shown a timing chart of the prior memory device. Assuming that the read command is generated at a timing t0 (A), the FAS and SAS is generated at a timing t1 (B) by the read control circuit 501. At the same time, the memory bank is activated in response to the read command, since the RO is also activated (C). In other words, the read-out data 801 is transferred to the first data amplifier. While the FAEN is generated at a timing t2 (D) by the first data amplifier control circuit 502. Accordingly, the read-out data is transferred to RWBUS in response to the FAEN (E). Then, the read-out data 801 arrives to the second data amplifier at a timing t4 through the RWBUS (F). In this connection, the read-out data is decided at a timing t5. Therefore, the second data amplifier control circuit delayed the SAS and generates the SAEN at a timing t6 (G). As a result, the read-out data 801 is transferred to data latch 213 (refer to FIG. 2) and outputted (H) at a timing t7. That is, a read-out time T2 in which the read-out data 801 is outputted is expressed by T2=(t7-t0).
In the aforesaid prior art semiconductor memory device, it is intended to realize a delay time of the SAEN of which value is quite short in length and requires an accurate adjustment in order to increase a data read-out speed during the data reading operation by the delay circuit 504 within the second data amplifier control circuit 503. It is a requisite condition in the semiconductor memory device to shorten a time until the read-out data 801 is outputted from the second data amplifier after the read command is inputted and to increase a data read-out speed from the memory block, and in order to attain these requirements, it becomes a requisite condition that at the timing for activating the second data amplifier amplifying data on the RWBUS is coincided with the timing of the data. However, a more increased setting of the timing of the SAEN outputted in delay by the second data amplifier control circuit 503 than that required may lead to a reduction in read-out speed of the semiconductor memory device and in the case that a delay time of the SAEN up to the limit point of the timing, there is a possibility that data on the RWBUS is not normally amplified at the second data amplifier and is not outputted normally. Due to this fact, although the delay time of the SAEN is accurately adjusted within the second data amplifier control circuit 503 and outputted as described above, as a practical problem, it is quite difficult to realize an accurate delay circuit due to various kinds of varying causes such as disturbance of the semiconductor element in its manufacturing stage, variation in power supply voltage and variation of surrounding air temperature and the like. Therefore, in the prior art semiconductor memory device, the data can be positively read out by applying a time surplus in an arrangement in which the timing of the SAEN is t5 in respect to the timing t3 of the RWBUS (near the second amplifier) in compliance with the aforesaid various causes.